This invention relates to a time-slot interchanger for a time-division multiplex switching system.
Different information streams (e.g., individual voice or data communications) often require different signal processing. This is particularly true in business communications systems, which typically handle a variety of types of communications. Some information streams may require no signal processing at all, while others may require different combinations of conferencing, echo cancellation, compression, etc.
Voice-communications-oriented switching systems, such as private branch exchanges (PBXs), typically route and distribute (switch) information streams by using time-division-multiplex (TDM) switching fabrics (e.g., buses), and use time-slot interchangers (TSIs) to extract information streams for signal processing from the TDM switching fabrics and to insert processed information streams back into the TDM switching fabrics. Each signal-processing function typically has a corresponding TSI that delivers the appropriate information stream to and from that function.
A problem lies with information streams that require the use of a plurality of signal-processing functions (for example, conferencing plus echo cancellation). They also require either additional TDM fabric time-slots to distribute partially processed streams between the plurality of signal-processing functions, or require additional control for signal-processing circuits that perform multiple signal-processing functions to effect the proper combination of signal-processing functions.
This invention is directed to solving these and other problems and disadvantages of the prior art. Generally according to the invention, a TSI is used to control not only time-slot access but also distribution of signals to signal-processing entities.
According to the invention, the TSI is designed for coupling to a plurality of entities (e.g., hardware circuits, or software or firmware functions) each one of which performs a different signal-processing function on signals input thereto. The TSI includes an arrangement for determining first and second information that specifies processing for first signals and different processing for second signals, respectively. This arrangement is illustratively a memory that stores the first and second information, but it could also illustratively be a communications link via which the TSI receives the first and second information, or even a logic function that generates the first and second information on its own. The TSI further includes an arrangement that responds to the first information by receiving the first signals in first time slots (e.g., in time slots of frames of a time-division multiplex communications medium) and inputting them for processing to zero or more of the entities which correspond to (e.g., perform) the processing specified by the first information, and that responds to the second information by receiving the second signals in second time slots and inputting them for processing to zero or more of the entities which correspond to the processing specified by the second information. (The processing may include a transformationless transfer, i.e., a no-op.) The first and the second information preferably includes control information for the entities, and the receiving and inputting arrangement conveys the control information included in the first information to ones of the entities, and conveys the control information included in the second information to others of the entities.
A single TSI configured according to the invention can serve a plurality of signal-processing functions, thus saving the expense of TSI replication. It can selectively configure the signal processing functions into various combinations and various sequences, so as to produce substantially any desired signal processing, and do so without needing a switching fabric to distribute partially-processed signals. The TSI is simple to implement: since it only extracts signals from time slots and enables appropriate signal-processing functions, it requires intelligent control only to set up the time slots and to enable the appropriate function controls. Illustratively, the TSIxe2x80x94as well as the signal-processing entitiesxe2x80x94may be implemented by a digital signal processor (DSP). The TSI also simplifies the design of some signal-processing entities. For example, in the case of the conferencing entity, the TSI sends all signals for each conference in sequence to the entity, before starting and sending any signals for any other conference, thereby allowing a single conference accumulator to support any number of conferences of any size. Moreover, the TSI control flexibility extends to multiple signal sources and destinations (e.g., signal-distribution media). For example, a TSI filling a T1 frame on a TDM bus may receive signals for 23B (traffic) channels from time slots of the TDM bus and may receive signals for the D (signaling) channel from a packet bus.